LHCb

Abstract:

We report a study of the semileptonic decay $D^0\to {\overline{K}}^0{\pi }^{-}{\mu }^{+}{\nu }_{\mu }$ based on a sample of $7.9{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured for the first time to be $\mathcal{B}(D^0\to {\overline{K}}^0{\pi }^{-}{\mu }^{+}{\nu }_{\mu })=(1.373\pm 0.020_{\mathrm{stat}}\pm 0.023_{\mathrm{syst}})\%$ , where the first uncertainty is statistical and the second is systematic. Based on the investigation of the decay dynamics, we find that the decay is dominated by the $K^{*}(892{)}^{-}$ resonance with the branching fraction measured to be $\mathcal{B}(D^0\to K^{*}(892{)}^{-}{\mu }^{+}{\nu }_{\mu })=(1.948\pm 0.033_{\mathrm{stat}}\pm 0.036_{\mathrm{syst}})\%$ . We also determine the hadronic form factors for the $D^0\to K^{*}(892{)}^{-}{\mu }^{+}{\nu }_{\mu }$ decay to be $r_V=V(0)/A_1(0)=1.46\pm 0.11_{\mathrm{stat}}\pm 0.04_{\mathrm{syst}}$ , $r_2=A_2(0)/A_1(0)=0.71\pm 0.08_{\mathrm{stat}}\pm 0.03_{\mathrm{syst}}$ , and $A_1(0)=0.609\pm 0.008_{\mathrm{stat}}\pm 0.008_{\mathrm{syst}}$ , where $V(0)$ is the vector form factor and $A_{1,2}(0)$ are the axial-vector form factors evaluated at $q^2=0$ . The $A_1(0)$ is measured for the first time in $D^0\to K^{*}(892{)}^{-}{\mu }^{+}{\nu }_{\mu }$ decay. Averaging the form factor parameters that we reported previously in $D^0\to K^{*}(892{)}^{-}(\to {\overline{K}}^0{\pi }^{-})e^{+}{\nu }_e$ and $D^0\to K^{*}(892{)}^{-}(\to K^{-}{\pi }^0){\mu }^{+}{\nu }_{\mu }$ decays, we obtain $r_V=1.456\pm 0.040_{\mathrm{stat}}\pm 0.016_{\mathrm{syst}}$ , $r_2=0.715\pm 0.031_{\mathrm{stat}}\pm 0.014_{\mathrm{stat}}$ , and $A_1(0)=0.614\pm 0.005_{\mathrm{stat}}\pm 0.004_{\mathrm{syst}}$ . This is the most precise determination of the form factor parameters to date measured in $D\to K^{*}(892)$ transitions, which provide the most stringent test on various theoretical models.

Abstract:

The ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{D}_s^{-}{K}^{+}{K}^{-}$ decay is observed for the first time using the data sample from proton-proton collisions recorded at a center-of-mass energy of 13 TeV with the LHCb detector, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$ . The ratio of branching fraction to that of ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{D}_s^{-}$ decays is measured as $0.0141\pm 0.0019\pm 0.0012$ , where the first uncertainty is statistical and the second systematic. A search for hidden-charm pentaquarks with strangeness is performed in the ${\mathrm{\Lambda }}_c^{+}{D}_s^{-}$ system. No evidence is found, and upper limits on the production ratio of $P_{c\overline{c}s}(4338{)}^0$ and $P_{c\overline{c}s}(4459{)}^0$ pentaquarks relative to the ${\mathrm{\Lambda }}_c^{+}{D}_s^{-}$ final state are set at the 95% confidence level as 0.12 and 0.20, respectively.

Abstract:

By analyzing a data sample containing events taken with the BESIII detector at the BEPCII storage ring in 2009, the resonance parameters are precisely measured using events. The mass of is determined to be ) MeV/ , and its full width is , where the first uncertainty is statistical, the second systematic, and the third for mass comes from mass uncertainty. These measurements improve the precision of mass by a factor of four and width by one order of magnitude over the previous individual measurements, and significantly boost our knowledge about the charmonium spectrum. Together with additional data events taken in 2012, the decay branching fractions of are measured as well, with precision improved by a factor of three compared to previous measurements. These decay branching fractions provide important inputs for the study of glueballs.

Abstract:

A sample of $pp$ collision data, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the ${\mathrm{\Xi }}_b^0$ baryon to that of the ${\mathrm{\Lambda }}_b^0$ baryon, $r_{\tau }\equiv {\tau }_{{\mathrm{\Xi }}_b^0}/{\tau }_{{\mathrm{\Lambda }}_b^0}$ . The value $r_{\tau }^{\mathrm{Run}2}=1.004\pm 0.009\pm 0.006$ is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain $r_{\tau }=1.004\pm 0.008\pm 0.005$ . Multiplying by the known value of the ${\mathrm{\Lambda }}_b^0$ lifetime yields ${\tau }_{{\mathrm{\Xi }}_b^0}=1.475\pm 0.012\pm 0.008\pm 0.009\mathrm{ps}$ , where the last uncertainty is due to the limited knowledge of the ${\mathrm{\Lambda }}_b^0$ lifetime. This measurement improves the precision of the current world average of the ${\mathrm{\Xi }}_b^0$ lifetime by about a factor of two, and is in good agreement with the most recent theoretical predictions.

Abstract:

The LHCb collaboration presents a novel suite of heavy-flavour jet substructure measurements at forward rapidity in proton-proton collisions at a centre-of-mass energy of s = 13 TeV. The jet mass is a perturbatively calculable probe of the virtuality of hard-scattered quarks and gluons, connecting small-distance quantum chromodynamics (QCD) with long-distance experimental measurement. The jet mass is dominated by nonperturbative corrections at small values, presenting an excellent test of QCD across a broad range of jet energies. Measuring heavy-flavour jet mass with a theoretically unambiguous flavour definition for the first time probes the gluon splitting mechanism for heavy-flavour production and offers tests of perturbative QCD at new levels of theoretical precision. Utilising the soft drop jet-grooming technique to access the perturbative jet core further enhances constraints on first-principles theory. Measurements of the jet mass for jets containing fully reconstructed B ± hadrons are reported with and without grooming. The unique phase space instrumented by LHCb offers a different quark-gluon fraction than at midrapidity. These results offer unparalleled tests of quark flavour and mass dependence in QCD and provide a baseline for future studies of heavy-flavour jet quenching in heavy-ion collisions.